Correlation problems in atomic and molecular systems III. Rederivation of the coupled‐pair many‐electron theory using the traditional quantum chemical methodst

Abstract The equations of the coupled‐pair many‐electron theory ( CPMET ) for the closed shell systems are rederived both in the spin‐orbital and orbital forms without the use of second quantization, Wick's theorem or the technique of Feynman‐like diagrams. Only the Slater rules are used for the calculation of necessary matrix elements. A comparison with earlier papers shows clearly the usefulness and conceptual simplicity of the mathematical methods of quantum field theory both in the derivation of the CPMET , in spin‐orbital form, and in the process of excluding spin variables.